As a method for preparing a heterocyclic aldehyde by oxidizing a heterocyclic alcohol, known is the method of preparing 3-pyridinecarbaldehyde or 4-pyridinecarbaldehyde by oxidizing 3-pyridinemethanol or 4-pyridinemethanol with sodium hypochlorite in the presence of a base and 2,2,6,6-tetramethylpiperidine-1-oxyl (see European Patent Publication No. 316783 and Org. Synth., 69, 212 (1990)).
Based on the above conventional method, the present inventors have studied the method of preparing a heterocyclic aldehyde by oxidizing a heterocyclic alcohol with hypohalogenous acid salt in the presence of a base and 2,2,6,6-tetramethylpiperidine-1-oxyl. As a result, as described below in Comparative Examples, the desired heterocyclic aldehyde is oxidized further and the selectivity and yield of the desired heterocyclic aldehyde is not satisfactory, as heterocyclic carboxylic acid is by-produced.
The present invention aims to provide a process for preparing a heterocyclic aldehyde by oxidizing a heterocyclic alcohol with high selectivity and high yield.